Chapter 16 Laboratory: Electrochemistry 285

Laboratory:

Electrochemistry

Electrochemistry is the study of the relationship between chemical energy and electrical

energy. Electrochemical processes involve two types of redox reactions. In the first type of

electrochemical process, applying an electric current causes a chemical reaction to occur.

For example, applying an electric current to water causes a chemical reaction that splits the

water into hydrogen gas and oxygen gas, an example of a process called electrolysis. In the

second type of electrochemical process, a chemical reaction produces an electric current.

For example, the chemical reaction that occurs in a standard alkaline AA cell produces

electric current that can be converted to light, heat, or mechanical energy.

Normally, a redox reaction occurs when an oxidizing agent and a reducing agent are

brought into contact. For example, placing an iron nail in a solution of copper sulfate causes

a spontaneous redox reaction. Iron atoms lose electrons (are oxidized) and enter solution as

iron ions, while copper ions gain electrons (are reduced) and are deposited as copper metal

on the nail.

In such redox reactions, electrons are transferred directly from one species to another.

However, if you physically separate the oxidizing agent (copper, in this example) and the

reducing agent (iron), the electron transfer that occurs during this redox reaction can be

redirected to flow through an external conductor, such as a wire. This is the basis of a

voltaic cell. Because the electric current is flowing through an external conductor rather

than contained within the cell, it is accessible to do useful work, such as lighting a light bulb

or powering an MP3 player.

Physical work (W) can be quantified as the product of the force (F) required to move an

object and the distance (d) the object is to be moved, or, mathematically, F = W · d. For

example, if you lift a box from the floor and place it on a shelf, the amount of work required

is the product of the force needed to lift the box times the distance the box is lifted. In its

new position on the shelf, the box has higher potential energy than it did when sitting on the

floor. (The work you did in lifting the box is converted to potential energy.) If the box falls

from the shelf to the floor, that higher potential energy is converted to kinetic energy, and the

potential energy of the box returns to its old, lower value.

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